1. Field of the Invention
The present invention relates to a piezoelectric element unit preferably used for such as a part of a driving device for driving a driven member and to a driving device therewith.
2. Description of the Related Art
Piezoelectric elements can mutually convert mechanical displacement to or from electronic displacement by utilizing piezoelectric effects or inverse piezoelectric effects. These piezoelectric elements are manufactured by molding and firing piezoelectric ceramics to obtain an element body, forming electrodes thereto, and further performing polarization treatment, for example.
Since the mechanical displacement obtained by the piezoelectric elements is comparatively small, the piezoelectric elements are preferably used as a driving device for which a precise and accurate control is required, for example. More specifically, the piezoelectric elements are used for lens drives, head drives of HDDs, head drives for ink jet printers, fuel injection valve drives, and the like.
For example, as a driving device with a piezoelectric element, one having a structure where a driving rod and a support table are respectively adhered to both ends of the piezoelectric element is disclosed (see Patent Literature 1 or so).
Solder is generally used for conventional multilayer piezoelectric elements to connect lead wires for wiring to external electrodes of piezoelectric elements. However, heat during solder connection may damage an element body composed of ceramic. Further, cracks due to difference in shrinkage coefficient between the element body and solder may be a problem when a cold-heat cycle is added while using the piezoelectric elements.
An attempt to use conductive paste instead of solder is proposed. However, there are problems in connection strength between the lead wires for wiring and the element body and in connection reliability due to weakness of humidity resistance.
[Patent Literature 1] JP Patent Application Laid Open No. 2002-119074